1. Field of the Invention
The present invention relates generally to methods and apparatus for thermally circulating a liquid, and more particularly to method and apparatus for thermally cycling a liquid in a direction counter to that of a normal thermal syphon without substantial limitation as to height.
2. Description of the Prior Art
In a substantially closed-loop liquid system, it is, of course, known that thermal syphon effect will transfer heat from a lower position to a more elevated position. By applying heat at a lower position, the liquid expands thereby lowering its density whereupon the heated liquid is displaced upward by more dense liquid at a lower temperature. This connection displacement induces a circulation whereby the heated liquid rises to the top of the system while the cooled liquid flows to the bottom. By extracting heat at an elevated location in the system, heat pumping by means of the thermal syphon is accomplished.
Obviously, the limitation of extracting heat at an elevated location while applying it at a lower location has limitations for many uses. For instance, solar heating is generally accomplished by collecting heat from solar radiation at an elevated position, such as a roof, and supplying it at a lower location, such as a basement heat sink.
Partial solutions to the problem of delivering heat from an elevated to a relatively lower position have been previously proposed. For instance, U.S. Letters Pat. Nos. 2,170,225 and 2,707,593 disclose means by which heat induced circulation contra to that of a thermal syphon is accomplished. However, these concepts are limited as to the height over which such circulation may be accomplished. For instance, in U.S. Letters Pat. No. 2,170,225, heat is applied to one vessel thereby displacing a liquid through a stand pipe into a higher vessel. The higher vessel and the stand pipe are connected by a closed loop of vessels and piping. Accordingly, the difference in level induces a flow of relatively heated liquid through the closed loop. Heat may be extracted at a lower portion of the closed loop and the liquid then returned to the first vessel. However, as a result of the heat extraction, the density of the liquid in different legs, i.e., the supply leg and the return leg, tends to offset the liquid level differential. When the height of the two legs is of a substantial magnitude, flow terminates even though there is a difference in liquid level between the stand pipes and second vessel. Accordingly, the prior art systems are height limited.